Mutant ‘super rats’ which cannot be killed by regular poisons are spreading across Britain, experts are warning.

The creatures, which look like normal rodents but eat toxic pellets ‘like feed’, have been discovered in Kent, the west country and now in Sussex.

The British Pest Control Association’s Richard Moseley told Metro: ‘Normal rats are being killed off by poison, so these resistant species are taking their place – it’s only natural that their numbers are expanding.

‘But they’re being found further afield than previously anticipated.

‘They eat poison like feed; you might as well be leaving out grain for them’.

There are an estimated 10.5million rats in Britain and they breed rapidly.

The gestation period is just 21 days and a female can have up to 14 pups at a time. Some breeding pairs can have 800 young in just two years.

Poison-resistant rats have been around for 50 years but researchers warn they are spreading rapidly. Mutants have been found in Sussex for the first time by researchers from the University of Huddersfield.

Last year, they found that 70 per cent of rats they tested in some counties were resistant to poisons routinely used by pest controllers. Researcher Dr Dougie Clarke told Metro a naturally-occurring mutation of genes was most likely to blame for the development of what he called ‘super rats’.

He said: ‘We’ve seen an increase in their prevalence. It’s now a big problem in some areas of the south of England.

‘The only solution is stronger poisons. There are concerns about poisoning of secondary animals and birds but, if it’s carefully controlled, it can be kept to an absolute minimum.’

Mr Moseley backed use of stronger poisons. He said: ‘Rats carry and spread diseases, so if their populations are left unchecked there can be a big public health risk.’

But Jeff Knott, from the Royal Society for the Protection of Birds, said: ‘We cannot afford to lock ourselves into a toxic arms race we can never win, as wildlife will be the loser.’